Process for the in situ blending of polymers

ABSTRACT

A process for the in situ blending of polymers comprising continuously contacting, under polymerization conditions, a mixture of ethylene and at least one alpha-olefin having at least 3 carbon atoms with a catalyst in at least two fluidized bed reactors connected in series, said catalyst comprising: 
     (i) a complex consisting essentially of magnesium titanium, a halogen, and an electron donor; 
     (ii) at least one activator compound for the complex having the formula AlR&#34; e  X&#39; f  H g  wherein X&#39; is Cl or OR&#39;&#34;; R&#34; and R&#39;&#34; are saturated aliphatic hydrocarbon radicals having 1 to 14 carbon atoms and are alike or different; f is 0 to 1.5; g is 0 or 1; and e+f+g=3; and 
     (iii) a hydrocarbyl aluminum cocatalyst, the polmerization conditions being such that ethylene copolymer having a high melt index in the range of about 0.1 to about 1000 grams per 10 minutes is formed in at least one reactor and ethylene copolymer having a low melt index in the range of about 0.001 to about 1.0 gram per 10 minutes is formed in at least one other reactor, each copolymer having a density of about 0.860 to about 0.965 gram per cubic centimeter and a melt flow ratio in the range of about 22 to about 70, and being admixed with active catalyst.

This application is a division of prior U.S. application Ser. No.271,639, filing date Nov. 16, 1988, now U.S. Pat. No. 5,047,468.

TECHNICAL FIELD

This invention relates to a process for polymerization whereby resinsare manufactured and blended in situ.

BACKGROUND ART

There has been a rapid growth in the market for linear low densitypolyethylene (LLDPE) particularly resin made under mild operatingconditions, typically at pressure of 100 to 300 psi and reactiontemperatures of less than 100° C. This low pressure process provides abroad range of LLDPE products for film, injection molding, extrusioncoating, rotational molding, blow molding, pipe, tubing, and wire andcable applications. LLDPE has essentially a linear backbone with onlyshort chain branches, about 2 to 6 carbon atoms in length. In LLDPE, thelength and frequency of branching, and, consequently, the density, iscontrolled by the type and amount of comonomer used in thepolymerization. Although the majority of the LLDPE resins on the markettoday have a narrow molecular weight distribution, LLDPE resins with abroad molecular weight distribution are available for a number ofapplications.

LLDPE resins designated for commodity type applications typicallyincorporate 1-butene as the comonomer. The use of a higher molecularweight alpha-olefin comonomer produces resins with significant strengthadvantages relative to 1-butene copolymers. The predominant higheralpha-olefins in commercial use are 1-hexene, 1-octene, and4-methyl-1-pentene. The bulk of the LLDPE is used in film products wherethe excellent physical properties and drawdown characteristics of LLDPEfilm makes this film well suited for a broad spectrum of applications.Fabrication of LLDPE film is generally effected by the blown film andslot casting processes. The resulting film is characterized by excellenttensile strength, high ultimate elongation, good impact strength, andexcellent puncture resistance.

These properties together with toughness are enhanced when thepolyethylene is of high molecular weight. However, as the molecularweight of the polymer increases, the processability of the resin usuallydecreases. By providing a blend of polymers, the propertiescharacteristic of high molecular weight resins can be retained andprocessability, particularly extrudability, can be improved.

Three major strategies have been proposed for the production of resinsof this nature. One is post reactor or melt blending, which suffers fromthe disadvantages brought on by the requirement of completehomogenization and attendant high cost. A second is the directproduction of resins having these characteristics via a single catalystor catalyst mixture in a single reactor. Such a process would providethe component resin portions simultaneously in situ, the resin particlesbeing ultimately mixed on the subparticle level. In theory, this processshould be the most rewarding, but, in practice, it is difficult toachieve the correct combination of catalyst and process parametersnecessary to obtain the wide diversity of molecular weights required.The third strategy makes use of multistage reactors, the advantage beingthat a quite diverse average molecular weight can be produced in eachstage, and yet the homogeneity of the single reactor process can bepreserved. Furthermore, two or more reactors running under their own setof reaction conditions permit the flexibility of staging differentvariables. To this end, many versions of multistage reactor processeshave been offered, but optimization has been elusive.

DISCLOSURE OF THE INVENTION

An object of this invention is to provide an optimized process for themultistage in situ blending of polymers to provide the desiredproperties as well as processability.

Other objects and advantages will become apparent hereinafter.

According to the present invention, a process for the in situ blendingof polymers has been discovered comprising continuously contacting,under polymerization conditions, a mixture of ethylene and at least onealpha-olefin having at least 3 carbon atoms with a catalyst in at leasttwo fluidized bed reactors connected in series, said catalystcomprising:

(i) a complex consisting essentially of magnesium, titanium, a halogen,and an electron donor; and

(ii) at least one activator compound for the complex having the formulaAlR"₃ X'_(f) H_(g) wherein X' is Cl or OR"'; R" and R"' are saturatedaliphatic hydrocarbon radicals having 1 to 14 carbon atoms and are alikeor different; f is 0 to 1.5; q is 0 or 1; and e+f+g=3; and

(iii) a hydrocarbyl aluminum cocatalyst, the polymerization conditionsbeing such that ethylene copolymer having a high melt index in the rangeof about 0.1 to about 1000 grams per 10 minutes is formed in at leastone reactor and ethylene copolymer having a low melt index in the rangeof about 0.001 to about 1.0 gram per 10 minutes is formed in at leastone other reactor, each copolymer having a density of about 0.860 toabout 0.965 gram per cubic centimeter and a melt flow ratio in the rangeof about 20 to about 70, and being admixed with active catalyst, withthe proviso that:

(a) the mixture of copolymer of ethylene and active catalyst formed inone reactor in the series is transferred to the immediately succeedingreactor in the series;

(b) in the reactor in which the low melt index copolymer is made:

(1) the alpha-olefin is present in a ratio of about 0.1 to about 3.5moles of alpha-olefin per mole of ethylene; and

(2) hydrogen is optionally present in a ratio of about 0.005 to about0.5 mole of hydrogen per mole of combined ethylene and alpha-olefin;

(c) in the reactor in which the high melt index copolymer is made:

(1) the alpha-olefin is present in a ratio of about 0.02 to about 3.5moles of alpha-olefin per mole of ethylene; and

(2) hydrogen is present in a ratio of about 0.05 to about 3 moles ofhydrogen per mole of combined ethylene and alpha-olefin; and

(d) additional hydrocarbyl aluminum cocatalyst is introduced into eachreactor in the series following the first reactor in an amountsufficient to restore the level of the activity of the catalysttransferred from the preceding reactor in the series to about theinitial level of activity in the first reactor.

DETAILED DESCRIPTION

The titanium based complex is exemplified by a complex having theformula Mg_(a) Ti(OR)_(b) X_(c) (ED)_(d) wherein R is an aliphatic oraromatic hydrocarbon radical having 1 to 14 carbon atoms or CDR' whereinR' is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbonatoms; each OR group is alike or different; X is Cl, Br, or I, ormixtures thereof; ED is an electron donor, which is a liquid Lewis basein which the precursors of the titanium based complex are soluble; a is0.5 to 56; b is 0, 1, or 2; c is 2 to 116; and d is 2 to 85. Thiscomplex and a method for its preparation are disclosed in U.S. Pat. No.4,303,771, issued on Dec. 1, 1981 which is incorporated by referenceherein.

The titanium compound, which can be used in the above preparations, hasthe formula Ti(OR)_(a) X_(b) wherein R and X are as defined forcomponent (i) above; a is 0, 1 or 2; b is 1 to 4; and a+b is 3 or 4.Suitable compounds are TiCl₃, TiCl₄, Ti(OC₆ H₅)Cl₃, Ti(OCOCH₃)Cl₃ andTi(OCOC₆ H₅)Cl₃.

The maximum compound has the formula MgX₂ wherein X is as defined forcomponent (i) above. Suitable examples are MgCl₂, MgBr₂, and MgI₂.Anhydrous MgCl₂ is a preferred compound. About 0.5 to 56, and preferablyabout 1 to 10, moles of the magnesium compound are used per mole oftitanium compound.

The electron donor used in the catalyst composition is an organiccompound, liquid at temperatures in the range of about 0° C. to about200° C. It is also known as a Lewis base. The titanium and magnesiumcompounds are both soluble in the electron donor.

Electron donors can be selected from the group consisting of alkylesters of aliphatic and aromatic carboxylic acids, aliphatic ketones,aliphatic amines, aliphatic alcohols, alkyl and cycloalkyl ethers, andmixtures thereof, each electron donor having 2 to 20 carbon atoms. Amongthese electron donors, the preferred are alkyl and cycloalkyl ethershaving 2 to 20 carbon atoms; dialkyl, diaryl, and alkyaryl ketoneshaving 3 to 20 carbon atoms; and alkyl, alkoxy, and alkylalkoxy estersof alkyl and aryl carboxylic acids having 2 to 20 carbon atoms. The mostpreferred electron donor is tetrahydrofuran. Other examples of suitableelectron donors are methyl formate, ethyl acetate, butyl acetate, ethylether, dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methylacetate, ethyl anisate, ethylene carbonate, tetrahydropyran, and ethylpropionate.

The activator compound can be represented by the formula AlR"_(e) X'_(f)H_(g) wherein X' is Cl or OR"'; R" and R"' are saturated aliphatichydrocarbon radicals having 1 to 14 carbon atoms and are alike ordifferent; f is 0 to 1.5; g is 0 or 1; and e+f+=3. Examples of suitableR, R', R", and R"' radicals are: methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, 2-methylpentyl,heptyl, octyl, isooctyl, 2-ethylhexyl, 5,5-dimethylhexyl, nonyl, decyl,isodecyl, undecyl, dodecyl, cyclohexyl, cycloheptyl, and cyclooctyl.Examples of suitable R and R' radicals are phenyl, phenethyl,methyloxyphenyl, benzyl, tolyl, xylyl, naphthyl, naphthal,methylnaphthyl.

Some examples of useful activator compounds are as follows:triisobutylaluminum, trihexylaluminum, di-isobutylaluminum hydride,dihexylaluminum hydride, di-isobutylhexylaluminum, trimethylaluminum,triethylaluminum, diethylaluminum chloride, Al₂ (C₂ H₅)₃ Cl₃, and Al(C₂H₅)₂ (OC₂ H₅). The preferred activators are triethylaluminum,triisobutylaluminum, and diethylaluminum chloride. The cocatalyst can beselected from among those compounds suggested as activators, which arehydrocarbyl aluminum compounds. Triethylaluminum and triisobutylaluminumare preferred cocatalysts.

While it is not necessary to support the complex or catalyst precursormentioned above, supported catalyst precursors do provide superiorperformance and are preferred. Silica is the preferred support. Othersuitable inorganic oxide supports are aluminum phosphate, alumina,silica/alumina mixtures, silica modified with an organoaluminum compoundsuch as triethylaluminum, and silica modified with diethylzinc. Atypical support is a solid, particulate material essentially inert tothe polymerization. It is used as a dry powder having an averageparticle size of about 10 to 250 microns and preferably about 30 toabout 100 microns; a surface area of at least about 3 square meters pergram and preferably at least about 50 square meters per gram; and a poresize of at least about 80 Angstroms and preferably at least about 100Angstroms. Generally, the amount of support used is that which willprovide about 0.01 to about 0.5 millimole of transition metal per gramof support and preferably about 0.2 to about 0.35 millimole oftransition metal per gram of support. Impregnation of the abovementionedcatalyst precursor into, for example, silica is accomplished by mixingthe complex and silica gel in the electron donor solvent followed bysolvent removal under reduced pressure.

The activator can be added to the titanium complex either before orduring the polymerization reaction. It is usually introduced beforepolymerization, however. In each reactor, the cocatalyst can be addedeither before or during the polymerization reaction; however, it ispreferably added neat or as a solution in an inert solvent, such asisopentane, to the polymerization reaction at the same time as the flowof ethylene, alpha-olefin, and hydrogen, if any, is initiated.

Useful molar ratios are about as follows:

    ______________________________________                                        Titanium                                                                      based catalyst                                                                             Broad             Preferred                                      ______________________________________                                        1. Mg:Ti     0.5:1   to 56:1   1.5:1 to 5:1                                   2. Mg:X      0.005:1 to 28:1   0.075:1                                                                             to 1:1                                   3. Ti:X      0.01:1  to 0.5:1  0.05:1                                                                              to 0.2:1                                 4. Mg:ED     0.005:1 to 28:1   0.15:1                                                                              to 1.25:1                                5. Ti:ED     0.01:1  to 0.5:1  0.1:1 to 0.25:1                                6. activator:Ti                                                                            0.5:1   to 50:1   1:1   to 5:1                                   7. cocatalyst:Ti                                                                           0.1:1   to 200:1  10:1  to 100:1                                 8. D:Al      0.05:1  to 25:1   0.2:1 to 5:1                                   ______________________________________                                    

The polymerization in each reactor is conducted in the gas phase using acontinuous fluidized bed process. A typical fluidized bed reactor isdescribed in U.S. Pat. No. 4,482,687 issued on Nov. 13, 1984. Thispatent is incorporated by reference herein. As noted, the reactors areconnected in series. While two reactors are preferred, three or morereactors can be used to further vary the molecular weight distribution.As more reactors are added producing different average molecular weightdistributions, however, the sharp diversity of which two reactors arecapable becomes less and less apparent. It is contemplated that theseadditional reactors could be used to produce copolymers with meltindices intermediate to the high and low melt indices previouslyreferred to.

The various melt indices can be prepared in any order, i.e., in anyreactor in the series. For example, the low melt index copolymer can bemade in the first or second reactor in the series and the high meltindex copolymer can be made in the first or second reactor as well. Theymust be made sequentially, however, to achieve the desired homogeneity.

The high melt index is in the range of about 0.1 to about 1000 grams per10 minutes and is preferably in the range of about 0.2 to about 600grams per 10 minutes. The low melt index is in the range of about 0.001to about 1.0 grams per 10 minutes and is preferably in the range ofabout 0.01 to about 0.2 gram per 10 minutes. The melt flow ratio is,however, about the same in both reactors, i.e., in the range of about 20to about 70. It depends on the density and melt index.

Melt index is determined under ASTM D-1238, Condition E. It is measuredat 190 ° C. and reported as grams per 10 minutes.

Melt flow ratio is the ratio of flow index to melt index. Flow index isdetermined under ASTM D-1238, Condition F. It is measured at 10 timesthe weight used in determining the melt index.

The titanium complex including the activator, the cocatalyst, theethylene monomer, any comonomers, and hydrogen, if any, are continuouslyfed into each reactor and ethylene copolymer and active catalyst arecontinuously removed from one reactor and introduced into the nextreactor. The product is continuously removed from the last reactor inthe series.

The alpha-olefin used to produce the polyethylene can have 3 to 10carbon atoms and preferably has 3 to 8 carbon atoms. Preferredalpha-olefins are 1-butene, propylene, 1-hexene, 1-octene,4-methyl-1-pentene. The density of the ethylene copolymer can be varieddepending on the amount of alpha-olefin comonomer added and upon theparticular comonomer employed. The greater the percent of alpha-olefincomonomer, the lower the density. The density of the polyethylene isabout 0.860 to about 0.955 gram per cubic centimeter.

The mole ratio of alpha-olefin to ethylene used to obtain the high meltindex and the low melt index is in the range of about 0.02:1 to about3.5:1. The ratios depend upon the amount of hydrogen, the amount ofcomonomer, and the density and melt index desired.

Both the comonomer and hydrogen can act as chain terminators. In subjectprocess, hydrogen is required in the high melt index reactor.

The mole ratio of hydrogen to combined ethylene and alpha-olefin in thehigh melt index reactor is in the range of about 0.05:1 to 3.5:1 and ispreferably in the range of about 0.5:1 to 2:1. In the low melt indexreactor the hydrogen is optional. If used, the mole ratio of hydrogen tocombined ethylene and alpha-olefin is in the range of about 0.005:1 to0.5:1 and is preferably in the range of about 0.01:1 to 0.3:1.

The fluidized bed polymerizations are conducted at a temperature belowthe sintering temperature of the product. The operating temperature isgenerally in the range of about 10° C. to about 115° C. Preferredoperating temperatures will vary depending upon the density desired. Lowdensity polyethylenes ranging in density from about 0.860 to about 0.910gram per cubic centimeter are preferably produced at an operatingtemperature of about 10° C. to about 80° C. The higher temperatures areused to achieve higher densities.

The high melt index reactor can be operated in the range of about 30° C.to about 105° C. and is preferably operated in the range of about 75° C.to about 90° C. The low melt index reactor can be operated in the samerange, the higher density resins utilizing the high end of the range.Insofar as pressures are concerned, the high melt index reactor can beoperated at about 100 to about 1000 psig and preferably at about 100 toabout 350 psig. The low melt index reactor can be operated at similarpressures.

Other conditions in the reactors can be about as follows:

    ______________________________________                                                               PREFERRED - BROAD RANGE RANGE                          ______________________________________                                        LOW MELT INDEX REACTOR                                                        1.  residence time                                                                              1 to 10      2 to 5                                             (hour):                                                                   2.  fluidizing gas                                                                               1 to 3.5    1.5 to 2.5                                         velocity                                                                      (foot per                                                                     second):                                                                  3.  low melt index                                                                             10 to 90      40 to 70                                           copolymer (per-                                                               cent by weight                                                                based on total                                                                copolymer pro-                                                                duced in two                                                                  reactors):                                                                HIGH MELT INDEX REACTOR                                                       1.  residence time                                                                              1 to 10      2 to 5                                             (hours):                                                                  2.  fluidizing gas                                                                               1 to 3.5    1.5 to 2.5                                         velocity                                                                      (foot per                                                                     second):                                                                  3.  high melt index                                                                            10 to 80      20 to 75                                           copolymer (per-                                                               cent by weight                                                                based on total                                                                copolymer pro                                                                 duced in two                                                                  reactors):                                                                ______________________________________                                    

An example of properties obtained from a two reactor (or two stage)process:

1. First reactor copolymer:

Melt Index=250 grams/10 min

Density=0.930 grams/cc.

Melt Flow Ratio=25

2. Second reactor copolymer

Melt Index=0.1 to 1.0 grams/10 min

Density=0.915 to 0.918 gram/cc

Melt Flow Ratio=25

3. Homogeneous mixture of both copolymers from second reactor:

Melt Index: 0.3 to 1.3 grams/10 min

Density=0.915 to 0.926 gram/cc

Melt Flow Ratio=50 to 68

The first reactor is generally smaller in size than the second reactorbecause only a portion of the polymer is made in the first reactor. Themixture of copolymer and an active catalyst is usually transferred fromthe first reactor to the second reactor via an interconnecting deviceusing nitrogen or second reactor recycle gas as a transfer medium.

A typical fluidized bed reactor can be described as follows:

The bed is usually made up of the same granular resin that is to beproduced in the reactor. Thus, during the course of the polymerization,the bed comprises formed polymer particles, growing polymer particles,and catalyst particles fluidized by polymerization and modifying gaseouscomponents introduced at a flow rate or velocity sufficient to cause theparticles to separate and act as a fluid. The fluidizing gas is made upof the initial feed, make-up feed, and cycle (recycle) gas, i.e.,comonomers and, if desired, modifiers and/or an inert carrier gas.

The essential parts of the reaction system are the vessel, the bed, thegas distribution plate, inlet and outlet piping, a compressor, cycle gascooler, and a product discharge system. In the vessel, above the bed,there is a velocity reduction zone, and in the bed, a reaction zone.Both are above the gas distribution plate.

Advantages of the product of subject process are the homogeneity anduniformity of the physical properties throughout the blend and the highstrength and toughness obtained without processing difficulty.

The invention is illustrated by the following examples.

EXAMPLES 1 to 3

The examples are carried out in accordance with the procedure describedabove.

A catalyst is prepared from a mixture of MgCl₂ /TiCl₃ /0.33AlCl₃/tetrahydrofuran supported on silica that has been dehydrated at 600° C.under a nitrogen atmosphere. [Note: one commercial form of TiCl₃contains an aluminum impurity due to the way the TiCl₄ is reduced toTiCl₃. This form is used in the examples. A form of TiCl₃, which doesnot contain aluminum, can also be used, e.g., a form known ashydrogen-reduced TiCl₃.] The support is treated with triethyl aluminumto passivate the surface through reaction with the remaining surfacesilanol groups, and with diethyl aluminum chloride and tri-n-hexylaluminum to moderate the kinetic reaction behavior of the catalyst andpromote good resin particle shape, i.e., substantial absence of particlewhich are "blown open" and a minimum of hollow particles.

The catalyst is made in a two-step process. The magnesiumchloride/titanium chloride/tetrahydrofuran salt is impregnated into thesilica support from the tetrahydrofuran solvent. The composition of thecatalyst precursor is as follows:

    ______________________________________                                        component      percent by weight                                              ______________________________________                                        TiCl.sub.3     5.97                                                           MgCl.sub.2     8.58                                                           tetrahydrofuran                                                                              15.00                                                          support (silica                                                                              70.45                                                          treated with                                                                  Al(C.sub.2 H.sub.5).sub.3)                                                                   100.00                                                         ______________________________________                                    

Analysis of the catalyst precursor:

    ______________________________________                                        component      percent by weight                                              ______________________________________                                        Ti             1.437                                                          Mg             2.188                                                          Al             1.182                                                          Cl             10.650                                                         tetrahydrofuran                                                                              15.000                                                         silica         69.543                                                                        100.000                                                        ______________________________________                                    

The precursor is contacted with diethyl aluminum chloride andtri-n-hexyl aluminum in an isopentane solvent; the residue is dried, andthe catalyst is ready for use in the first reactor. The diethyl aluminumchloride and tri-n-hexyl aluminum are added in amounts based on thetetrahydrofuran content. The diethyl aluminum chloride is added first ata mole ratio of 0.2/1 based on tetrahydrofuran. The tri-n-hexyl aluminumis then added at a mole ratio of 0.2:1 based on the tetrahydrofuran. Thefinished catalyst is dried to a free flowing powder having the followingcomposition:

    ______________________________________                                        component         percent by weight                                           ______________________________________                                        Ti                1.24                                                        Mg                1.888                                                       Al (total)        3.43                                                        Cl (from Ti and Mg)                                                                             9.19                                                        tetrahydrofuran   12.94                                                       diethyl aluminum chloride                                                                       4.31                                                        tri-n-hexyl aluminum                                                                            10.14                                                       ______________________________________                                    

Polymerization is initiated in the first reactor by continuously feedingthe above catalyst and a cocatalyst, triethylaluminum (TEAL), into afluidized bed of polyethylene granules together with the gaseouscomonomers and hydrogen. The TEAL is dissolved in isopentane (5 percentby weight TEAL). The resulting copolymer mixed with active catalyst iswithdrawn from the first reactor and transferred to the second reactorusing nitrogen as a transfer medium. The second reactor also has afluidized bed of polyethylene granules. Again gaseous comonomers andhydrogen are introduced into the second reactor where they come incontact with the copolymer and catalyst from the first reactor.Additional cocatalyst is also introduced. The copolymer product iscontinuously removed. Variables with respect to catalyst and conditionsas well as the properties of the resin product are set forth in theTable.

                                      TABLE                                       __________________________________________________________________________                        Example                                                                       1             2             3                                                 Reactor                                                                            Reactor  Reactor                                                                            Reactor  Reactor                                                                            Reactor                  Catalyst            I    II       I    II       I    II                       __________________________________________________________________________    Ti loading (millimole per grams of                                                                0.25 0.25     0.25 0.25     0.25 0.25                     support)                                                                      Mg/Ti (atomic ratio)                                                                              3.0  3.0      3.0  3.0      3.0  3.0                      Ti (weight % based on weight                                                                      1.0  1.0      0.94 0.94     1.0  1.0                      of toal catalyst)                                                             Al (weight % based on weight                                                                      2.88 2.88     2.73 2.73     2.87 2.87                     of total catalyst)                                                            TEAL (weight % based on weight of                                                                 5    5        5    5        5    5                        silica)                                                                       Reaction Conditions                                                           Reactor temperature (°C.)                                                                  86   86       86   86       80   82                       Reactor pressure (psia)                                                                           314.7                                                                              314.7    314.7                                                                              314.7    314.7                                                                              314.7                    Hydrogen/ethylene (mole ratio)                                                                    1.21 0.151    1.47 0.0819   1.93 0.0443                   Comonomer           1-butene                                                                           1-butene 1-butene                                                                           1-butene 1-hexene                                                                           1-hexene                 Comonomer/ethylene (mole ratio)                                                                   0.319                                                                              0.378    0.317                                                                              0.366    0.131                                                                              0.1847                   Ethylene partial pressure (psia)                                                                  82   143      79   154      73   147125                   Nitrogen (% of total reactor pressure)                                                            33   29       30   28       21   42                       Fluidization velocity (feet per second)                                                           1.8  2.0      1.8  2.0      1.8  2.0                      Percent of total production                                                                       62   38       55   45       39   61                       Fluidized bed weight (pounds)                                                                     60   140      60   140      60   120                      Production rate (pounds per hour)                                                                 28.3 45.8     23.7 42.8     18.0 46                                           (Est.)        (Est.)        (Est.)                        Fluidized bed volume (cubic feet)                                                                 3.9  9.8      3.6  9.5      4.2  9.2                      Space/time/yield (pounds per hour per                                                             7.2  4.7      6.6  4.5      4.3  5.0                      cubic foot)                                                                   residence time (hours)                                                                            2.1 (Est.)                                                                         3.1      2.5 (Est.)                                                                         3.3      3.3 (Est.)                                                                         2.6                      TEAL feed rate      110  125      113  138      166  83                       (cubic centimeters per hour)                                                  Catalyst feeder     100  --       250  --       250  --                       (revolutions per minute)                                                      Resin properties              final         final          final              Melt Index (grams per 10 minutes)                                                                 122  1.0   3.9                                                                              242  0.3  1.3 325  0.07  0.23               Flow Index          2953 145  145 --   59   59  --   11.6  11.6               Melt Flow Ratio     24.3 24   35  24   25   46  25   25    51                 Density (gram per cubic centimeter)                                                               0.930                                                                              0.920                                                                              0.925                                                                             0.931                                                                              0.920                                                                              0.925                                                                             0.930                                                                              0.915 0.922              Ash (weight % based on the weight                                                                 --   0.025                                                                              0.025                                                                             --   0.031                                                                              0.031                                                                             --   0.022 0.022              of the product)                                                               Bulk density of product                                                                           20.4 19.0 19.1                                                                              22.4 19.0 19.7                                                                              18.9 18.0  17.4               (pounds per cubic foot)                                                       Average particle size (inch)                                                                      0.0195                                                                             0.030                                                                              0.0288                                                                            0.0148                                                                             0.0297                                                                             0.0297                                                                            0.0137                                                                             0.0296                                                                              0.0296             Fines (weight % based on the weight                                                               2.7  0.5  2.4 3.4  0.6  3.0 2.2  0.0   2.0                of the product - less than 120 mesh)                                          Residual Ti (parts per million)                                                                   --   1.4  1.4 --   1.4  1.7 --   1.4   2.0                __________________________________________________________________________

Notes to Table:

1. DEAC=diethylaluminum chloride

2. THF=tetrahydrofuran

3. Total catalyst=Ti complex, i.e., titanium, magnesium, halogen, DEACand THF; silica support; and cocatalyst

4. Residence time=average time each active catalyst particle is in thereactor.

5. Melt Index is determined under ASTM D-1238, Condition E. It ismeasured at 190° C.

6. Flow Index is determined under ASTM D-1238, Condition F. It ismeasured at 10 times the weight used in the melt index test above.

7. Melt Flow Ratio is the ratio of the Flow Index to the Melt Index.

8. The resin properties set forth under Reactor II are estimated. Theresin properties set forth under final are the average values for theproducts of Reactors I and II.

EXAMPLE 4

A rubber-modified high density polyethylene adapted for filmapplications is prepared.

The procedure of examples 1 to 3 is repeated. The different variablesfollow:

    __________________________________________________________________________                                    Final Product                                 Catalyst             Reactor I                                                                          Reactor II                                                                          From Reactor II                               __________________________________________________________________________    Ti loading (millimole per gram of support)                                                         0.25 0.25  --                                            Mg/Ti (atomic ratio) 3    3     --                                            TEAL (weight % based on weight of                                                                  5    5     --                                            silica)                                                                       Al (weight % based on weight of                                                                    2.88 2.88  --                                            total catalyst)                                                               Reaction Conditions                                                           Reactor temperature (°C.)                                                                   105  30    --                                            Reactor pressure (psia)                                                                            315  315   --                                            Hydrogen/ethylene (mole ratio)                                                                     0.09 0.005 --                                            Comonomer            1-butene                                                                           propylene                                                                           --                                            Comonomer/ethylene (mole ratio)                                                                    0.028                                                                              2.3   --                                            Ethylene partial pressure (psia)                                                                   120  52    --                                            Percent of total production                                                                        75   25    --                                            Fluidization velocity (feet per second)                                                            1.5  2.3   --                                            TEAL (parts per million in bed)                                                                    350  350   --                                            Resin Properties                                                              Melt Index (gram per 10 minutes)                                                                   0.5  0.05  0.25                                          Melt Flow Ratio      30   63    90                                            Density (gram per cubic centimeter)                                                                0.950                                                                              0.865 0.928                                         Average Particle Size (inch)                                                                       0.022                                                                              0.03  0.031                                         Fines (weight % based on the weight                                                                5    0     1.5                                           of the product - less than 120 mesh)                                          Bulk density of product (pounds per                                                                20   18    20                                            cubic feet)                                                                   Residual Ti (parts per million)                                                                    4    1.8   3                                             __________________________________________________________________________

We claim:
 1. A process for the in situ blending of polymers wherein ahigher density and higher melt index ethylene copolymer matrix isprepared in a high melt index reactor and a lower density and lower meltindex ethylene copolymer is then incorporated into the ethylenecopolymer matrix in a low melt index reactor comprising continuouslycontacting, under polymerization conditions, a mixture of ethylene andat least one alpha-olefin having at least 3 carbon atoms in at least twofluidized bed reactors connected in series, with a catalystcomprising:(i) a silica supported complex consisting essentially ofmagnesium, titanium, a halogen, and an electron donor; (ii) at least oneactivator compound for said complex having the formula AlR"_(e) X'_(f)H_(g) wherein X' is Cl or OR"; R' and R" are saturated aliphatichydrocarbon radicals having 1 to 14 carbon atoms and are the same ordifferent; f is 0 to 1.5; g is 0 or 1; and e+f+g=3; and (iii) ahydrocarbyl aluminum cocatalyst,the polymerization conditions being suchthat an ethylene copolymer having a high melt index in the range ofabout 0.2 to about 0.5 gram per 10 minutes is formed in at least onereactor and an ethylene copolymer having a low melt index in the rangeof about 0.001 to about 0.2 gram per 10 minutes is formed in at leastone other reactor, each copolymer having a density of from about 0.860to about 0.965 gram per cubic centimeter and a melt flow ratio in therange of from about 20 to about 70, and being admixed with activecatalyst, with the provisos that: (a) the mixture of high melt indexcopolymer of ethylene and active catalyst formed in one reactor in theseries is transferred to an immediately succeeding reactor in the seriesin which low melt index polymer is made; (b) in a reactor in which thelow melt index copolymer is made:(1) said alpha-olefin is present in aratio of about 0.1 to about 3.5 moles of alpha-olefin per mole ofethylene; and (2) hydrogen is present in a ratio of about 0.001 to about0.3 mole of hydrogen per mole of combined ethylene and alpha-olefin; (3)additional hydrocarbyl aluminum cocatalyst is added in an amountsufficient to restore the level of the activity of the catalysttransferred from the preceding reactor in the series to about thecritical level of activity in the first reactor in the series; (4) otherthan the active catalyst referred to in proviso (a), no additionalcatalyst is added; (c) in a reactor in which high melt index copolymeris made:(1) said alpha-olefin is present in a ratio of about 0.02 toabout 3.5 moles of alpha-olefin per mole of ethylene; and (2) hydrogenis present in a ratio of about 0.05 to about 2 moles of hydrogen pertotal moles of ethylene and alpha-olefin.
 2. The process of claim 1wherein the said activator compound is at least one of triethylaluminum,triisobutylaluminum, and diethylaluminum chloride.
 3. The process ofclaim 1 wherein the aluminum cocatalyst is at least one oftriethylaluminum and triisobutylaluminum.
 4. The process of claim 1wherein the complex has the formula Mg_(a) Ti(OR)_(b) X(ED)_(d) whereinR is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbonatoms or COR' wherein R' is an aliphatic or aromatic hydrocarbon radicalhaving 1 to 14 carbon atoms, each OR group is the same or different; Xis Cl, Br, or I, or mixtures thereof; ED is a liquid Lewis base electrondonor in which the precursors of the titanium based complex are soluble;a is 0.5 to 56; b is 0, 1, or 2; c is 1 to 116; and d is 2 to
 85. 5. Theprocess of claim 1 wherein the said electron donor is tetrahydrofuran.6. The process of claim 1 wherein there are two reactors in the series.7. The process of claim 1 wherein a high density polyethylene isprepared in the high melt index reactor and an ethylene/propylenecopolymer is prepared in the low melt index reactor in intimateadmixture with said high density polyethylene.
 8. The process of claim 1wherein the process is conducted in the gas phase in each reactor.